The present state of the ferroconcrete art assumes, in the classical dimensioning theory for flexurally stressed structural members, an interrelationship between tensile and compressive forces by way of the shear strength of the concrete. This assumption presupposes that the reinforcement steel sustaining the tensile forces in the tension zone of the flexurally stressed structural member has bonding adhesiveness. Only when this adhesiveness is assured does the reinforcement steel transfer its forces to the surrounding concrete which retransmits them via its shear capacity to the compression zone of the concrete.
The bonding ability of the reinforcing rod under tension in the concrete is a significant, cost-intensive weak point whose at least partial solution has been tried by a twisting of the rods (British Pat. No. 15,946/1908), profiling, rolling, convolutions, welded ladder-type inserts (German Pat. No. 907,587), welded-on junction pieces, upsetting, superposed sleeves (German laid-open specification No. 1,609,910) etc. In this way it has actually been possible to reduce the bonding length.
My Austrian Pat. No. 310,397 shows another possibility according to which short anchor ties are welded at least onto the ends of the reinforcing rods. Even though in this manner the bonding lengths of the reinforcing rods can be completely omitted and high-grade reinforcement steel can thereby be saved, since the short reinforcements can be produced from lower-quality steel, there still remains the need for manufacturing these short reinforcements and welding them on.
Finally, Austrian Pat. No. 309,757 deals with a shortening of the bonding length and proposes for this purpose, in the case of reinforcing mats, to dispose transverse rods within that half of the bonding length which lies at the end of the longitudinal rods.